Adjustable cooling system for airplane electronics

ABSTRACT

Airplane ground service equipment includes an air conditioning system for an airplane and also a fluid cooling system for airplane electronics which detachably connects to a first port and a second port on the airplane. The fluid cooling system includes a first connector, a second connector, and a fluid conduit therebetween, the first and second connectors being adapted to be connected to the first and second ports, respectively, such that the connection of the ports to the connectors completes a fluid circuit. A fluid pump directs fluid through the fluid conduit, and a heat exchanger in the fluid conduit removes heat from the fluid circuit and transfers it into the air conditioning system of the ground support equipment. A temperature regulation mechanism stabilizes the temperature of the fluid in the fluid conduit to compensate for changes in the amount of heat that is drawn from the airplane electronics.

This application is a non provisional of provisional application Ser.No. 60/984,002 filed Oct. 31, 2007 (Atty. Docket No. 21585-P1) andprovisional application Ser. No. 61/036,727 filed Mar. 14, 2008 (Atty.Docket No. 50-003 ITW 21585-P2).

CROSS-REFERENCE TO RELATED APPLICATIONS

The present patent application is one of a set of commonly ownedapplications filed on the same day as the present application, sharingsome inventors in common, and relating to airplane ground supportequipment and carts. The other applications in this set, listed here,are hereby incorporated by reference into the present application: “AMulti-Voltage Power Supply for a Universal Airplane Ground SupportEquipment Cart,” James W. Mann, III and David Wayne Leadingham (Ser. No.______, Atty. Doc. No. 50-002 ITW 21608U); “A Frame and Panel System forConstructing Modules to be Installed on an Airplane Ground SupportEquipment Cart,” Jeffrey E. Montminy, Brian A. Teeters, and KytaInsixiengmay (Ser. No. ______, Atty. Doc. No. 50-004 ITW 21588U); “ASystem of Fasteners for Attaching Panels onto Modules that are to beInstalled on an Airplane Ground Support Equipment Cart,” Jeffrey E.Montminy, Brian A. Teeters, and Kyta Insixiengmay (Ser. No. ______,Atty. Doc. No. 50-005 ITW 21587U); “Airplane Ground Support EquipmentCart Having Extractable Modules and a Generator Module that is Separablefrom Power and Air Conditioning Modules,” James W. Mann, III and JeffreyE. Montminy (Ser. No. ______, Atty. Doc. No. 50-006 ITW 21586U); “AnAdjustable Air Conditioning Control System for a Universal AirplaneGround Support Equipment Cart,” James W. Mann, III, Jeffrey E. Montminy,Benjamin E. Newell, and Ty A. Newell (Ser. No. ______, Atty. Doc. No.50-007 ITW 21606U); “A Compact, Modularized Air Conditioning System thatcan be Mounted Upon an Airplane Ground Support Equipment Cart,” JeffreyE. Montminy, Kyta Insixiengmay, James W. Mann. III, Benjamin E. Newell,and Ty A. Newell (Ser. No. ______, Atty. Doc. No. 50-008 ITW 21583U);and “Maintenance and Control System for Ground Support Equipment,” JamesW. Mann, III, Jeffrey E. Montminy, Steven E. Bivens, and David WayneLeadingham (Ser. No. ______, Atty. Doc. No. 50-009 ITW 21605U).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to the field of cooling usingfluid coolants, and more particularly to airplane ground supportequipment that, in addition to providing air and electrical conditioningservices to airplanes, is also able to provide airplanes requiringliquid coolants with polyalphaolefin (PAO) or other similar liquidcoolants at controlled temperatures and pressures to cool airplaneelectronics.

2. Description of the Related Art

When an airplane is on the ground with its engines shut down, theairplane is typically unable to provide power for its electrical systemsand chilled air for its air conditioning systems; and some airplanes arealso unable to provide liquid coolant for some critical electronic (or“avionic”) components. It is customary to connect such a groundedairplane to an airplane ground support equipment system. Such a systemmay have its components mounted upon a mobile equipment cart that iscalled an airplane ground support equipment cart and that may be parked,placed, or mounted conveniently close to an airplane requiring groundsupport. Such a cart typically contains an air conditioner that canprovide conditioned and cooled air to an airplane plus an electricalpower converter that can transform power drawn from the local power gridinto power of the proper voltage (AC or DC) and frequency required bythe airplane. Such an airplane ground support equipment cart may alsocontain a diesel engine connected to an electrical generator thatenables the cart to provide both air conditioning and also electricalpower for an airplane without any connection to the local power grid.And if an airplane requires a source of cooled liquid for itselectronics, some carts may also include a source of liquid coolant.

In the past, particularly with regard to military airplanes, such groundsupport equipment carts have been custom designed to meet thespecialized needs of a single particular type or class of airplane.Hence, a cart designed to support the specific requirements and needs ofa first type or class of airplane cannot be used to support thediffering specific requirements and needs of other types or classes ofairplanes. Different airplanes typically may require different pressuresand volumes of cooled air, different amounts of electrical power,different electrical voltage levels, and different electricalfrequencies (or direct current). And different airplanes typically mayrequire differing pressures and volumes of cooled liquid for use incooling onboard electronics. Accordingly, every airport must be suppliedwith as many different types of ground support equipment carts as thereare different types or classes of airplanes that may land and take offat each airport or military base. Problems arise when more airplanes ofa particular type arrive at a specific location than there are groundsupport equipment carts suitably designed to service the needs of thatparticular type or class of airplane.

To be more specific, some airplanes require their ground supportequipment to provide considerably more airflow at higher pressures thando other airplanes having smaller interiors. Some airplanes requiretheir electrical power to be adjusted to 115 volts of alternatingcurrent (A.C.) which alternates, or flows back and forth, 400 times eachsecond (115 volts, 400 Hz A.C.). Other airplanes require 270 voltsdirect current (270 volts, D.C.) that does not flow back and forth. Yetother airplanes require a source of 28 volts of direct current (28volts, D.C.). And airplanes also differ in the amount of electricalpower that they draw.

Some airplanes, particularly jet fighters, need an additional source ofcooling from their ground support equipment in the form of a liquidcoolant that is applied to the so-called avionics systems, includingelectronics and radar systems. This liquid is typically apolyalphaolefin, or PAO, heat transport fluid or liquid coolant. Thisfluid is propelled by a pump through one or more heat exchangers withinthe airplane that cool the liquid using cool air that is presentwhenever the airplane's turbo fan propulsion engine is in operation. Thecooled liquid is then passed through the avionics.

When such an airplane's engine is not in operation, the PAO fluid mustbe cooled in some other manner to prevent the avionics from overheating.One way to accomplish this is to include in the airplane ground supportequipment a PAO pump and a mechanism for cooling the PAO heat transportfluid. A pair of hoses can connect the airplane's PAO fluid system tothe ground support equipment, and a circular flow between the airplaneand the ground support equipment is established whereby the PAO fluidflows out of the avionics in the airplane to the ground supportequipment where the pump propels the fluid through some form of heatexchange mechanism to cool the fluid, which then flows back into theairplane and into the avionics. Since the temperature and pressure andfluid flow volume requirements for PAO cooling may vary from one type orclass of airplane to the next, a PAO cooling system designed to meet thespecialized PAO cooling needs of one airplane will not necessarily meetthe somewhat different needs of another type or class of airplane.

As an example of an airplane cart arrangement that provides air andelectrical conditioning for an airplane, PCT patent application No.PCT/US2006/043312 (Intl. Pub. No. WO 2007/061622 A1 published on May 31,2007) discloses an airplane ground support cart that has a modulardesign of its electrical conditioning components. This cart provides airconditioning and electrical power conversion as well as optionalelectrical power generation services to airplanes. FIG. 5 reveals thatthe cart disclosed in this patent application may receiveinterchangeable, modular power conversion modules. Thus, a module 72,which generates 3-phase 115 volt 400 Hz A.C. power, may be removed andreplaced with a module 78, which generates 270 volt D.C. power. FIG. 6illustrates that this cart may also accept a module 92, which generates28 volt D.C. electrical power.

FIG. 2 of the above PCT patent application illustrates a typicalarrangement of the mechanical components of a dual air conditioningsystem within an airplane ground support equipment cart 14. The airconditioner's mechanical components are spread all across the entirelength of the cart 14. Two sets of condenser coils 34 are positioned atone end of the cart 14; and the thickness of the coils 34 and theirhousing, together with the thickness of the associated cooling fans,occupies roughly one-fifth of the cart's overall length. A filter andupstream evaporation coil 30 and a downstream evaporation coil 40 andoutlet connection 42 (to which can be attached a duct leading to anairplane) are positioned at the other extreme end of the cart 14,occupying somewhat less than one-fifth of the cart's overall length. Ablower fan 32, a discharge plenum 38, and two compressors 36 are shownpositioned in the central portions of the cart 14. These mechanicalcomponents of the air conditioning system are not confined within arectangular module within a portion of the volume of the cart 14—thesecomponents are spread all across the cart 14 and thus cannot beconveniently removed from the cart for servicing or for use away fromthe cart 14. Other cart components, such as a diesel engine 54 andgenerator 56 (shown in FIG. 4 of the PCT application) and an electricalpower converter unit 72 (shown in FIG. 5 of the PCT application) aresqueezed in among the air conditioning components wherever there isroom. This intermixing of non-air-conditioning components with theair-conditioning components greatly complicates servicing of all thecomponents, since they are all crowded into the same cramped space. Aservice man working on the air conditioner compressors or blowers mayfind the diesel engine 54 and generator 56 are in the way of thesecomponents, for example.

The air conditioning systems of such a conventional ground supportequipment system is also designed to provide a particular volume ofcooled air at a particular temperature and pressure to a particular typeor class of airplane. If such a system has its cool air ducted into someother type or class of airplane, too much or too little air will flowfrom the air conditioner system, and this will throw off the balance ofthe air conditioning system, causing the air to be cooled too little ortoo much and possibly causing icing of the internal evaporator arrays ordamage to the airplane. And the temperature and pressure provided maynot be proper for some other type or class of airplane. Likewise, theelectrical systems may not be able to supply the needs of differingtypes or classes of airplanes, and the PAO liquid cooling system may notbe properly balanced when used to cool the avionics of differing typesor classes of airplanes.

SUMMARY OF THE INVENTION

An embodiment of the invention relates to ground support equipmentincluding an air conditioning system for an airplane and also includinga fluid cooling system for airplane electronics which detachablyconnects to a first port and a second port on the airplane. The fluidcooling system includes a first connector, a second connector, and afluid conduit there between, the first and second connectors beingadapted to be connected to the first and second ports, respectively,such that the connection of the ports to the connectors completes afluid circuit. A fluid pump directs fluid through the fluid conduit, anda heat exchanger in the fluid conduit removes heat from the fluidcircuit and transfers it into the air conditioning system of the groundsupport equipment. A temperature regulation mechanism stabilizes thetemperature of the fluid in the fluid conduit to compensate for changesin the amount of heat that is drawn from the airplane electronics.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view of an embodiment of a universal airplaneground support equipment cart having a modular design.

FIG. 2 is an isometric view of the cart shown in FIG. 1 with the dieselengine and generator module portion that forms the back portion of thecart shown separated from the rest of the cart.

FIG. 3 is an isometric view of an electrical conversion module of thecart shown in FIG. 1 to illustrate how it may be slid out of and awayfrom the side of the cart for maintenance purposes or to be replacedwith a different module.

FIG. 4 is a perspective view of a two-stage air conditioning module thatis mounted on the front portion of the cart shown in FIG. 1, the airconditioning module shown with both of its microchannel condenser coilsupporting doors shown swung open to reveal its internal structuraldetails.

FIG. 5 is a schematic diagram illustrating the flow path of air as itflows through the two-stage air conditioning module shown in FIG. 4.

FIG. 6 is a schematic diagram illustrating the refrigerant circulationpaths within the first, or “pre-cool,” air conditioning unit within thetwo-stage air conditioning module shown in FIG. 4, and also showing aheat exchanger which transfers heat from a separate PAO cooling system(not shown) to the refrigerant within this first air conditioning unit.

FIG. 7 is a schematic diagram illustrating the refrigerant circulationpaths within the second, or “post-cool,” air conditioning unit withinthe two-stage air conditioning module shown in FIG. 4.

FIG. 8 is a schematic diagram of a PAO cooling system within the airconditioning module shown in FIG. 4 which transfers heat from anairplane to the first, or “pre-cool,” air conditioning unit within thetwo-stage air conditioning module shown in FIG. 4.

FIG. 9 presents an exploded, perspective view of four plate finevaporator arrays assembled into a square array, mounted within arectangular frame, and attached to a funnel-shaped duct that conveyscooled air to the external piping which leads to an airplane.

FIG. 10 presents a perspective view of the assembly of plate finevaporator arrays shown in FIG. 9 mounted between two funnel-shapedducts that spread the air to be cooled uniformly across the surface ofthe plate fin evaporator arrays.

FIG. 11 presents a perspective view of a microchannel condenser unit ofthe type used in pairs and mounted upon the two doors of the two-stageair conditioning module shown in FIG. 4.

FIG. 12 presents a partly sectional view, taken along the lines A-A inFIG. 10, of a microchannel condenser unit illustrating interior detailsof the air channels.

FIG. 13 is a block diagram illustrating the signal-carrying bus and theway in which it interconnects the power generating module, two powerconverter modules, and the two-stage air conditioning module with acontrol module that includes a display screen with eight pushbuttons anda universal control and diagnostics processor.

FIG. 14 is a combined flow diagram and state diagram illustrating thenormal start-up and run procedures of the overall system and alsoillustrating the warning, alarm, and shut down states.

FIG. 15 is a simplified schematic diagram (combining elements taken fromFIGS. 5, 6, 7, and 8) illustrating the air flow and the refrigerantcirculation paths in the pre-cool and post-cool air conditioning unitsand also in the PAO cooling system, and identifying in particular theeight feedback control loops and controllers that control the operationof these systems and also the temperatures and pressures and set-pointsthat provide input signals to these controllers.

FIG. 16 is a state diagram illustrating the operation of the compressorswithin the two air conditioning units.

FIG. 17 is a flow diagram illustrating how the operation of the blowerfan which blows air through the two air conditioner units and into theairplane is automatically controlled through the use of a variablefrequency drive for the motor that drives the blower fan.

FIG. 18 is a schematic diagram showing the connection of the twocompressors, the two-speed condenser cooling fan, and the blower fan'svariable frequency drive to a three-phase source of 380 to 500 volt, 50to 60 Hz electrical power and also showing control signals for thecompressors, cooling fan, and blower fan.

FIG. 19 illustrates and names all of the significant system statesignals (temperatures, pressures, etc.) that enter the air conditioningand PAO processor, and it also illustrates all of the significant on/offand 0-to-10 volt output control signals which that processor generatesto control all of the air conditioning processes, thereby allowing theair conditioner system to respond flexibly and properly to widelyvarying load conditions that can be caused by different types andclasses of airplanes.

FIG. 20 presents a block diagram of all the menus and submenus that maybe displayed on the face of the control module's display screen,together with the navigation paths between these menus and submenus.

FIG. 21 presents a view of the main menu.

FIG. 22 presents a view of a help menu that appears when the “Help” itemis selected on the main menu shown in FIG. 21.

FIG. 23 presents a view of a menu that appears when the airplane “T-50Golden Eagle” is selected on the main menu shown in FIG. 21.

FIG. 24 presents a view of a help menu that appears when the “Help” itemis selected on the “T-50 Golden Eagle” menu shown in FIG. 23.

FIG. 25 presents a view of a maintenance menu that appears when the“Maintenance” item is selected on the main menu shown in FIG. 21.

FIG. 26 presents a view of a scrollable data logging menu and viewingwindow that appears when the “Data Log Screen” item is selected on themaintenance menu shown in FIG. 25.

FIG. 27 illustrates a view of a pre-cool air conditioning unit's statusvalues that appears when the “A/C Maintenance” item is selected on themaintenance menu shown in FIG. 25.

FIG. 28 illustrates a view of one of two actuator status and relaystatus screens that appear when the “Relay Status Screen” item isselected on the maintenance menu shown in FIG. 25—the values displayedcorrespond to the more important output control signals generated by theair conditioning and PAO processor shown in FIG. 19.

FIG. 29 presents an exploded isometric view of the control module'sdisplay screen, illustrating that the screen is covered by metalscreening that serves as a radio frequency wave blocking screen.

DETAILED DESCRIPTION OF THE INVENTION

The detailed description which follows is broken into two sections.Section A presents an introduction to the environment of the presentinvention, which relates to the design of a PAO liquid cooling systemthat is incorporated and integrated into the air conditioning system ofa modularized universal airplane ground support equipment cart (FIGS.1-3). Section B presents a detailed description of the PAO liquidcooling system in the context of the complete ground support airconditioning system, including that system's internal mechanical details(FIGS. 1-4, 9-12, and 29), air flow details (FIG. 5), refrigerant andPAO coolant flow path details (FIGS. 6-8), electronic control systemdetails (FIGS. 13-19), and display system and human interaction details(FIGS. 20-28). While the focus of the present invention is the PAOliquid cooling system and the related control systems (disclosedprimarily in FIGS. 6, 8, and 15), the PAO system is so closelyintegrated into the overall air conditioning system that the two systemsare described below as a single, integrated system.

A. Modular and Universal Airplane Ground Support Equipment Cart

Airplane ground support equipment carts are wheeled, towable carts orfixed mounted (permanently or temporarily) devices that provide airconditioning, avionics equipment liquid cooling, and electrical powerconversion and generation services to airplanes whose engines are shutdown. These carts preferably should be conveyed by military and otherairplanes to airports and military bases all over the world, so it wouldbe convenient and an advantage to have this equipment be no larger thana standard military equipment conveyance palette. However, many suchcarts today do not fit one standard palette, and this reduces thenumbers of ground support equipment that is available in the field.Traditionally, such ground support equipment carts arecustom-designed—they provide such services to only one type or class ofairplane. Hence, different carts must be provided for each differenttype of airplane. Also traditionally, the air conditioning componentsmounted on such carts are so bulky that they occupy the entire area ofthe cart, making it necessary to sandwich electrical power conversionand other components wherever there is room and thereby making itextremely awkward to service or replace such cart-mounted components.

The present invention is embodied in a universal airplane ground supportequipment cart—universal in the sense that it is designed to service thevaried needs of a variety of types and classes of airplanes, rather thanjust one type or class. This ground support equipment cart is alsomodular—its components are rectangular modules that may be easilyseparated or removed from the cart for service or exchange. The modulesmay also be used independently of the cart, and modules not needed for aparticular type of airplane may be readily removed and used elsewhere,standing by themselves, in a highly flexible manner. Such a cart 10 andseveral of its modules—an electrical power generation module 14, anelectrical power conversion module 20, and a dual air conditioningmodule 400 (which also provides PAO liquid cooling)—are illustrated insimplified form in FIGS. 1-3. (Much more detailed drawings of thesecomponents are included in this application and also in the relatedapplications cited above).

In use, the cart 10 is mounted near or drawn up to an airplane (notshown) by a suitable tractor or truck (not shown). An operator connectsan air conditioning plenum or air duct 26 from the dual air conditioningmodule 400 to a cooled air input port (not shown) on the airplane. Andif the airplane has avionics or other electronic components that requirea supply of liquid coolant, then the operator also connects a pair ofPAO liquid coolant conduits 28 from the air conditioning module 400 to apair of PAO ports on the airplane. The operator then uses a suitableelectrical power cable (not shown) to connect an electrical power outputport or receptacle (not shown in FIGS. 1-3) on the electrical powerconversion module 20 to a matching port or cable on the airplane. Tosupply the varying needs of different types of airplanes, there may beas many as two electrical power conversion modules 20 the cart 10, afirst module 20 having both a 115 volt, 400 Hz AC power output port andalso a separate 270 volt DC power output port, and a second module 1308(FIG. 13) having a 28 volt DC power output port (one or the other ofthese modules 20 or 1308 may be removed from the cart 10).

Next, with reference to FIG. 13, the operator depresses a “Start”pushbutton 1316 on the front panel of a control module 22 having adisplay screen 24 that then displays a main menu such as that shown inFIG. 21. If the airplane is a T-50 Golden Eagle, the operator depressesone of four pushbuttons 1304 that is adjacent the label “T-50 GoldenEagle” on this menu (FIG. 21), and then the operator depresses one offour pushbuttons 1302 that is adjacent the label “Start” on a “T-50”menu that then appears (FIG. 23). In response, all of the modulesautomatically reconfigure themselves as needed to service this specifictype of airplane with air conditioning of the proper pressure and volumeof air, with electrical power of the proper type, voltage, andfrequency, and with liquid coolant (if needed). If the operator selectsthe wrong type of airplane, pressure and air flow measurements candetect this and shut down the system, illuminating a colored statuslight 1314 to signal an error and displaying an appropriate errormessage on the control panel 24 to the operator. The system is haltedwhen the operator depresses a “Stop” pushbutton 1318 on the front of thecontrol 22 or a pushbutton 1302 or 1304 that is adjacent the label“Stop” on one of the display screen 24 menus.

A universal airplane ground support equipment cart is designed toprovide flexible support for the needs of many different types andclasses of airplanes having widely varying air conditioning and liquidcooling and electrical power support needs. The present invention canprovide different pressures and volumes of cooled air and cooled liquidto different airplanes, and it can provide different types andquantities of electrical power to different airplanes. It also providesa simplified, integrated control panel where airplane service personnelcan simply select the type of airplane that is to be serviced and havethe various appliances on the cart automatically configured to optimizethe support for that particular type of airplane.

A modular airplane ground support equipment cart is one where thedifferent support systems provided by the cart are each confined torugged, compact, optionally EMI shielded, rectangular modules that maybe easily removed, serviced, replaced, and used stand-alone separatefrom the cart and its other modular components.

In the cart 10, for example, a two-stage air conditioning module 400contains all of the air conditioning components of the cart 10,including a liquid PAO cooling system. An electrical power convertermodule 20 contains the power conversion components of the cart 10,including a 270 volt D.C. supply and a 115 volt 400 Hz A.C. supply; andthe module 20 may be replaced or supplemented with another module 1308(FIG. 13) that includes a 28 volt D.C. supply, providing up to threedifferent types of electrical power conversion in accordance with thespecialized needs of different types and classes of airplanes.

A power supply module 14 contains a diesel engine and a generator forproducing 60 cycle, three-phase, 460 volt electrical power when the cartcannot be conveniently hooked up to a 360 to 500 volt, 50 or 60 cycleA.C., three phase supply provided by the local power grid. The powersupply module 14 is confined to one end of the cart 10 and may bedetached from the cart 10, as is illustrated in FIG. 2.

Any or all of these modules 14, 20, 400, and 1308 may optionally beequipped with an internal transformer (not shown) that transforms theincoming high voltage electrical power down to 120 volts or 240 volts at50- or 60-Hz and feeds this low voltage to standard, weather protectedoutlets (not shown) which can be used to provide power to hand tools andto portable lighting equipment and the like, with ground faultprotection also provided to these appliances.

As is illustrated in FIG. 13, a control module 22 is mounted on the cart10 above the power converter module 20. The control module 22 has on itsfront panel a pair of start and stop pushbuttons 1316 and 1318, coloredstatus lights 1314, and a display screen 24 having sets of fourpushbuttons 1302 and 1304 positioned adjacent the display screen 24'sleft and right sides. When turned on, the display screen 24 presents amain menu display, shown in FIG. 21, which permits airplane maintenancepersonnel to select the type of plane that is to be serviced bydepressing one of the adjacent pushbuttons 1302 and 1304. A maintenancemenu display, shown in FIG. 25, permits service personnel to view and(in some cases) to alter the state of the air conditioning and PAOmodule 400, the electrical power converter modules 20 and 1308, and thepower supply module 14. As is illustrated schematically in FIG. 13, allof the modules 14, 20, 22, 400, and 1308 are automatically networkedtogether by a network 1312 when they are installed upon the cart 10. Inaddition, each of the modules 14, 20, 22, 400, and 1308 is equipped witha network jack (not shown) that can be connected to an external portablecomputer (not shown) which can then serve as the control module anddisplay for all of the modules, with mouse clicks on the menus shown inFIGS. 20 to 28 replacing depressions of the pushbuttons 1302 and 1304.

The cart 10 is optionally mounted upon two wheel and axle truckassemblies 18 and 19. In the space on the cart 10 between the powergeneration module 14 and the two-stage air conditioning module 400, oneor both of the electrical power converter modules 20 and 1308 may beslid into place and attached to the cart 10, as is illustrated in FIGS.2 and 3. (If both are installed, they may be on opposite sides of thecart, as shown, or they may be installed one above the other.)

If the power generation module 14 is not required for a particularairplane support task, the module 14 and the wheel and axle truckassembly 19 beneath the module 14 may be completely detached from therest of the cart 10, as is illustrated in FIG. 2, and removed to be usedentirely separately elsewhere, wherever a portable source of 60 Hz, 460volt, three-phase power is required. As illustrated in FIGS. 2 and 3,the electrical power converter modules 20 and 1308 may be slid out ontracks and locked in position to give service personnel convenientaccess for the servicing of these modules 20 and 1308 and their internalelectrical and electronic components. They may also be removed forrepair or for use elsewhere as stand-alone power converters, or they maybe replaced with different power converter modules that generatedifferent voltages and frequencies as needed for servicing differentairplanes.

B. Two-Stage Air Conditioning and PAO Liquid Cooling System

The two-stage air conditioning system and PAO liquid cooling system thatis described below has many valuable attributes. Among others: It canachieve a 30-second air conditioner startup, rather than the manyminutes that are required to start up conventional airplane groundsupport equipment air conditioners, due to the close control that isexerted over all aspects of the system and inherently low refrigerationsystem charge by minimizing internal volume of the refrigeration system(see FIG. 15 and the accompanying descriptive material presented below).Since the digital control algorithms may be varied dynamically by theprocessor 1900 to suit unusual conditions, the air conditioner can stilloperate even if many sensors and controllers are inoperative based uponmemory of past operations which can be relied upon to predict conditionsin place of actual sensor readings to give control guidance. And as willbe explained, an operator indicates on a menu (FIG. 18) which type orclass of airplane is to be serviced. If, when the air conditioner isstarted up initially at a lower blower speed than the final blowerspeed, the pressure and air flow measurements captured by thetemperature, pressure, and power consumption measurement sensors do notcorrespond to that choice of type or class of airplane, the airconditioner can shut down and give the operator an appropriate warningmessage that the wrong type of airplane has most likely been selected.Other examples of the system's attributes are set forth below. Animproved user interface is presented in an appendix to this application,where start and stop buttons and colored lamps are added to the displayto improve its usability and the menus are adjusted accordingly.

Referring now to FIGS. 4 through 12, the internal mechanical and fluidflow path details of the two-stage air conditioning module 400 areshown. The module 400 contains two air conditioning stages—a pre-coolair conditioner 520 (shown in FIGS. 5 and 6) and a post-cool airconditioner 522 (shown in FIGS. 5 and 7). The flow of air along a path500 through the two air conditioners 520 and 522 stages are described inFIG. 5. The flow of coolant through the two air conditioners 520 and 522stages are illustrated in FIG. 6 (pre-cool air conditioner 520) and inFIG. 7 (post-cool air conditioner 522). The pre-cool air conditioner 520has associated with it a PAO liquid cooling system 700. FIG. 8illustrates the flow of avionics liquid coolant through this PAO liquidcooling system 700 and between the system 700 and avionics 825 within anairplane 823. The mechanical details of each of the air conditioner'splate fin evaporator arrays are illustrated in FIGS. 9 and 10, and themechanical details of each of the air conditioner's micro-channelcondenser coils are illustrated in FIGS. 11 and 12.

FIG. 4 presents a perspective view of the two-stage air conditioningmodule 400 as seen from its rear side 402, with the air duct 26 thatconveys air conditioned air to the airplane (not shown) shown extendingto the right (in FIGS. 1 and 2, the air duct 26 extends to the left).The side 402 is accordingly the side of the module 400 that is notadjacent the electrical power converter modules 20 and 1308 and thecontrol module 22 when these modules 400, 20, 22, and 1308 are allmounted on the cart 10, as shown in FIG. 1. Accordingly, the module400's rear side 402 is always accessible for servicing the module 400and is not blocked by the presence of the other modules.

A hinged, louvered door 404 is shown swung open from the rear side 402(FIG. 4) of the module 400, and this door gives service personnelunfettered access to all the air conditioning and PAO components withinthe module 400 for service and maintenance procedures, but would not beleft open during operation. A second hinged, louvered door 408 is shownswung upwards from the top side of the module 400. This door 408 givesservice personnel access to the PAO system 700 components which aremounted near the top of the module 400.

The two louvered doors 404 and 408 each support a pair of thin,microchannel air conditioner condenser coils 406 and 410 the details ofwhich coils are shown in FIGS. 11 and 12 (discussed below). Each pair oftwo condenser coils 406 and 410 is associated with a respective one ofthe two air conditioners 520 and 522 stages mounted within the airconditioning module 400. A two-speed condenser fan 414 blows air out ofa fan portal 418 in one side 416 of the air conditioning module 400—theside that is not connected by the air duct 26 to the airplane. When boththe doors 404 and 408 are closed, the condenser fan 414 sucks airthrough both of the pairs of microchannel condenser coils 406 and 410,cooling the refrigerant within the two condenser coils 406 and 410. Thefan 414 blows the air heated by passage through the two condenser coils406 and 410 out the fan portal 418 on the side 416 of the cart 10 awayfrom where service personnel viewing the display screen 24 or connectingup the air duct 26 or the PAO liquid coolant conduits 28 would normallystand. With reference to FIGS. 15 and 18, the fan 414 has low speed 415and high speed 417 fan control signals which are generated by acontroller 1518 which is implemented as an algorithm within the airconditioning and PAO processor 1900. The controller responds to theambient temperature and to various temperature and pressure signalsshown in FIGS. 5, 6, and 7 by varying the fan 414 from off to low speedto high speed as needed to aid the processor in maintaining the properoperation of the two air conditioners 520 and 522. This is another wayfor the system to adjust rated capacity, a way that is especially usefulwhen the system is running at low capacities—that is, at low ambientconditions.

FIG. 5 presents a schematic diagram of the air pathway 500 taken by airwhich is cooled, dehumidified, and compressed as it passes through thetwo-stage air conditioning module 400. Outside air shown at 501 issucked through the pre-cool air conditioner 520 by a blower 508 whichthen propels the air through the post-cool air conditioner 522 andthrough the air duct 26 from which it emerges as a stream of cooled,dehumidified, pressurized air that flows directly into the airplane (notshown).

The pre-cool air conditioner 520 includes as components a firstevaporator array 504 (FIGS. 4 and 5) and a pair of the microchannelcondenser coils 406 (FIG. 4) plus other components all of which areshown together in FIG. 6 (described below). The post-cool airconditioner 522 includes as components a second evaporator array 514(FIGS. 4 and 5) and a second pair of the microchannel condensers 410(FIG. 4) plus other components all of which are shown in FIG. 7(described below). The two air conditioners 520 and 522 are essentiallyidentical except that the pre-cool air conditioner 520 includes a PAOheat exchanger 602 (FIGS. 6 and 8) that absorbs heat from the PAO liquidcoolant circuit 700 shown in FIG. 8.

Referring now to FIGS. 4 and 5, air 501 that is to be dehumidified andcooled flows along the air pathway 500 first through an air filter 502and next through the pre-cool air conditioner's 520 plate fin evaporatorarray 504, where the air is partially cooled and dehumidified. The airnext flows through a narrowing plenum 505 (FIG. 4) and then onwards tothe blower 508, which propels the air forward at increased pressure. Theair next passes through an outlet cone 510 (FIG. 4) designed to convertvelocity pressure coming from the blower 508 into static pressure(static regain) before making a turn through an elbow 512 (FIG. 4). Theair then flows into an expansion chamber or air funnel 513 (FIG. 10)which contains a baffle plate that spreads out the air so that the airpasses uniformly through all parts of the post-cool air conditioner522's plate fin evaporator array 514. The further cooled anddehumidified air then flows through a narrowing plenum 516 (FIGS. 4, 9,and 10) and through a circular coupling 518 (FIGS. 4, 9, and 10) out theair duct 26 (FIGS. 1, 4, and 5) and onwards to the interior of theairplane (not shown).

The blower 508 is driven by a variable-speed electric motor 506 thespeed of which motor is controlled by the frequency of the motor 506'sincoming electric power. A voltage-to-frequency converter 525 accepts aserialized digital control signal 1706 which specifies the motor 506'sfrequency and which is supplied by an air conditioner and PAO processor1900 (a real-time process control computer system—see FIG. 19). Theconverter 525 responds to that signal 1706 by varying the frequency ofthe input power to the motor 506 up and down in accord with thefrequency called for by the control signal 1706 based upon a controlalgorithm that monitors the output pressure (measured by the pressuresensor 526). The processor 1900 receives a 0-to-10 volt pressuremeasurement signal from a pressure sensor 526 that measures the pressurewithin the ring 518 and air duct 26 that supplies cooled air to theairplane (not shown). With reference to FIGS. 5 and 15, the processor1900 compares the pressure read by the pressure sensor 526 to aset-point desired pressure, which may vary from one type and class ofplane to the next, and then adjusts the control signal 1706 so as toadjust the blower 508's speed to a setting that maintains the pressurewithin the air duct 26 at or close to the proper pressure that isrequired to cool the particular type or class of airplane.

In FIG. 15, a controller 1514 is shown symbolically comparing a setpointpressure Psp to the air duct pressure measured by the pressure sensor526 and then generating the signal 1706 which controls the blower 508speed. The controller 1514 is actually implemented digitally within theprocessor 1900. The controller 1514 would typically have a proportionalcomponent to minimize the pressure error and an integral component todrive that pressure error towards zero over time. The airplane selectionprocess, described below in conjunction with the selection menu shown inFIG. 21, can alter the pressure setpoint Psp value as well as othertemperature setpoint Tsp values (described below) to customize the airconditioner and PAO controllers shown in FIG. 15 to the specific needsand requirements of differing types and classes of airplanes. When oneof the pushbuttons 1304 adjacent the display screen 24 (FIG. 13) isdepressed, for example, to program the modules on the cart 10 to servicethe T-50 Golden Eagle (see FIG. 21), the optimal temperature Tsp andpressure Psp setpoints for that airplane are selected by the airconditioning and PAO processor 1900 and are placed into a memory ofsetpoints 1317 (FIG. 13).

FIG. 17, which is described below, describes other aspects of the blower508 control algorithm in somewhat greater detail.

Differential pressure sensors 528, 530, 532, and 534 enable theprocessor 1900 to monitor the pressure drop across various airconditioning system components. These pressure readings are collected bythe processor 1900 and saved in a data log 1319 (FIG. 13) and are usedlater on for maintenance purposes. For example, an excessive pressuredrop across the air filter 502 measured by the differential pressuresensor 528 signals that it soon will be time to clean or replace the airfilter 502. Excessive pressure drop across the evaporator arrays 504 or514 measured by the differential pressure sensors 530 and 534 can signalicing of an evaporator array that is running too cold or a cloggedevaporator array that requires cleaning. The pressure drop across theblower 508, when compared to the signal 1706 frequency value and alsothe electrical power applied to the blower 508 (as measured by voltagesensor 1720 and current sensor 1722 both shown in FIG. 18) can indicatethe condition of the blower and its motor and whether servicing isneeded. This information is saved in the processor 1900's data log 1319(FIG. 13).

Pressure sensor 536 (see FIG. 5) monitors the outside air pressure,which is recorded by the processor 1900 in the data log 1319. Pressuresensor 543 (FIG. 5) monitors the output air pressure generated by theblower 508 which is also the air pressure within the air plenums, apressure that can also be recorded by the processor 1900 in the data log1319. RTD (resistor temperature device) temperature sensors 538, 540,542, and 544 monitor the air temperature before and after the air passesthrough the two evaporator arrays 504 and 514. These temperaturemeasurements are fed into the processor 1900 which records them in thedata log 1319 and can use them for predictive maintenance. As an option,some or all of these temperatures and pressures may be used to adjustthe amount of cooling that is generated by each of the two airconditioners, as is illustrated in FIG. 15.

FIGS. 6 and 7 present detailed schematic diagrams of the pre-cool airconditioner 520 and the post-cool air conditioner 522. In one embodimentof the invention, the refrigerant tubing used in the construction ofthese air conditioners 520 and 522 is ACR copper tubing, with brazedjoints and with many sweated fittings used to achieve a curved path ofrefrigerant flow. In another embodiment, aluminum tubing is used insteadof copper tubing. A tube bender is then used in lieu of many sweatedjoints, and this reduces the number of parts used on each system, agreat cost reducer. A great feature of aluminum is that it makes thesystem very lightweight and cost less when compared to copper, asaluminum weighs about 70% less than copper and cost approximatelyone-third as much. In addition, the use of flared fittings would alsoallow assembly to take place with pre-made lengths and tubeconfigurations where the assembly technician would just need to turn awrench instead of waiting for a skilled worker certified in copperbrazing. This would also make field repairs much quicker than everbefore.

FIG. 6 presents a schematic diagram of the pre-cool air conditioner 520.With reference to FIG. 6, a compressor 601 compresses the refrigerantand sends it along a path 604 to one of the pair of condenser coils 406,where the refrigerant is cooled by air flowing through the airconditioning module 400 under the impetus of the condenser fan 414, aswas described above, where the refrigerant cools and becomes liquefied.The air conditioning and PAO processor 1900 (FIG. 19) sends out a firston/off pre-cool shutoff signal to a solenoid valve 603 and an on/offpre-cool compressor on signal 1702 which can turn the pre-coolcompressor 601 on and off (see FIGS. 18 and 19) and which can shut downthe pre-cool air conditioner 520 by shutting off the compressor 601 andisolating the compressor 601 from refrigerant migration by closing thesolenoid valve 603. The shutdown algorithm will then close all therefrigeration valves 620, 638, and 632 (FIG. 6) to further preventrefrigerant migration back to the compressor 601.

The cooled and liquefied refrigerant next flows past a charging valve608, a filter dryer 606, and a sight glass 610 over a path 612 to abrazed plate heat exchanger 614 (FIGS. 4 and 6) that is mounted at thevery bottom of the air conditioning module 400, as is shown at 614 inFIG. 4. The brazed plate heat exchanger 614 has a multi-purpose in itsdesign: it serves as a liquid refrigerant accumulator that collects anyexcess liquid refrigerant and any excess oil that may be in the suctionline between the compressor 601 and the evaporator array 504 to preventdamage to the compressor 601 (which is designed to pump vapor). Thebrazed plate heat exchanger 614 also serves as a liquid suction linesub-cooler that sub cools the liquid refrigerant by allowing theexpanded gasses flowing along the path 628 and 630 and entering thecompressor 601 to absorb heat from the liquid refrigerant in the lines612 and 618 and in the brazed plate heat exchanger 614. The liquid lineside of the brazed plate heat exchanger 614 acts as a refrigerantreceiver, accumulating excess refrigerant charge on the condenser sideof the system. The brazed plate heat exchanger 614 increases thecapacity and efficiency of the cooling system at high load conditions.Finally, the brazed plate heat exchanger is used to control the suctionline superheat, allowing the evaporators to be fully flooded. Floodingthe evaporators allows high cooling capacity from the evaporators aswell as increasing the evaporator capacity while maintaining higherrefrigerant temperature which helps avoid evaporator frosting.

The path 618 conducts the cooled but still liquefied refrigerant to anelectronically controlled expansion valve 620 that is controlled by a0-to-10 volt signal generated by the processor 1900. The liquidrefrigerant flows through the expansion valve 620 into the low pressure,cool side of the refrigerant circuit, where the liquid begins tovaporize and absorb heat from its surroundings. This boiling liquidpasses first through the PAO heat exchanger 602, where it cools theliquid PAO fluid flowing into a line 622 and out a line 624 which lineslead to the PAO fluid circuit (shown at 700 in FIG. 8). The boilingrefrigerant flows onward over the path 626 to the plate fin evaporatorarray 504 essentially identical to the evaporator array 514 shown inFIG. 9, where the refrigerant cools the air that is sucked into themodule 400 at 501 (FIG. 5) from the outside air, through the air filter502 and the plate fin evaporator array 504 and into the blower 508. Thegaseous refrigerant leaves the plate fin evaporator array 504 and flowsalong the path 628 back through the brazed plate heat exchanger 614 andover the path 630 back to the compressor 601 where it is once againcompressed and fed into the pair of condenser coils 406 to becompressed, thus completing the passage of refrigerant through thisvapor compression cycle.

Combined temperature and pressure transducers monitor the condition ofthe refrigerant throughout this circuit. An RTD (resistor temperaturedevice) temperature and pressure transducer 607 monitors the temperatureand pressure of the liquid refrigerant as it leaves the condenser coils406 and enters the brazed plate heat exchanger 614. A second RTDtemperature and pressure transducer 616 monitors the temperature andpressure of the liquid refrigerant as it leaves the brazed plate heatexchanger 614 over the path 618 and flows through the expansion valve620. Another temperature and pressure transducer 634 monitors thetemperature and pressure of the gaseous, cooled refrigerant flowing outof the plate fin evaporator array 504. A pair of temperature andpressure transducers 609 and 611 monitors the temperature and pressureof the gaseous refrigerant entering the compressor 601 and also leavingthe compressor 601. The refrigerant temperature and pressure readingsgenerated by all of these transducers 607, 616, 634, 609, and 611 andalso the pre-cool condenser air output temperature measured by the RTDair temperature transducer 540 are fed into the air conditioning and PAOprocessor 1900 (see FIG. 19) where these temperatures and pressures maybe stored in the data log 1319 (FIG. 13).

The refrigerant temperatures measured by the RTD temperature transducers609, 616 and 634 and the air temperature measured by the pre-cool airconditioner output RTD temperature transducer 540 are also used for airconditioner control purposes, as is illustrated in FIG. 15.

The pre-cool air conditioner output temperature measured by the RTDtemperature transducer 540 is compared to a setpoint temperature,typically 10 degrees Celsius or thereabouts, by means of a controller1506 which is implemented as a digital process control algorithm withinthe air conditioner and PAO processor 1900. As the desired outputtemperature is adjusted by the user, this setpoint temperature can bealtered. This controller 1506 is given both proportional and integraloutputs which are summed and used (as a 0-to-10 volt signal) to controlan electronic exhaust gas bypass valve 638 (EGBV—FIGS. 6 and 15) which,to the degree it is open, permits compressed, hot gas to bypass thecondenser coils 406 and the expansion valve 620 and to flow directlyfrom the compressor 601 into the evaporator array 501, thereby raisingthe temperature and boiling excess liquid refrigerant within theevaporator array 504. The processor 1900 continuously adjusts this EGBvalve 638 to maintain the air temperature at the pre-cool airconditioner's plate fin evaporator array 504 outlet at or just abovefreezing so that the evaporator array 504 is not permitted to ice up.

The refrigerant temperature (measured by the RTD transducer 616) at theoutlet of the electronic expansion valve (EEV) 608, which is the inletinto the PAO heat exchanger 602 and plate fin evaporator array 504, isfed into another controller 1502 (FIG. 15), which is also implemented asa digital process control algorithm within the air conditioner and PAOprocessor 1900. This controller 1502 is also given both proportional andintegral outputs which are summed and used (as a 0-to-10 volt signal) tocontrol an electronic evaporator array pressure regulator valve EPR 632(FIGS. 6 and 15) which valve controls how much cooled, expanded, gaseousrefrigerant is permitted to enter the compressor 601. In this manner,the temperature at the input to the evaporator array 504 and the PAOliquid heat exchanger 602 are controlled and maintained at a setpointvalue Tsp, which value is fed into the controller 1502 (FIG. 15). Thissetpoint is typically kept at 1 degree Celsius. As the desired unitoutput temperature is adjusted by the user, this setpoint may bealtered. The air conditioning and PAO processor 1900 maintains thissetpoint value, as well as other similar temperature and pressuresetpoint values, in a memory for setpoints 1317 (FIG. 13) where thesevalues may sometimes be altered when different types and classes ofairplanes are being serviced.

The refrigerant temperature (measured by the RTD transducer 616) at theoutlet of the electronic expansion valve (EEV) 608, which is the inletinto the PAO heat exchanger 602 and plate fin evaporator array 504, iscompared to the refrigerant temperature (transducer 634) at the outletof the plate fin evaporator array 504 by another controller 1504, whichis also implemented as a digital process control algorithm within theair conditioner and PAO processor 1900. This controller 1504 mayinitially be given both proportional and integral outputs which aresummed and used (as a 0-to-10 volt signal) to control the electronicexpansion valve EEV 608 (FIGS. 6 and 15) which valve controls to whatextent the entire evaporator array 504 is thoroughly wetted andparticipating in the cooling process. Experiments have shown, however,that the controller 1504 may have to be programmed in a nonlinearmanner, with the control parameters worked out empirically by experimentand varying from a simple proportional and integral controller to somedegree. The EEV 608 is adjusted to maximize the effective cooling areaof the evaporator array, as is indicated by a maximum temperature dropacross the plate fin evaporator array 504. The air conditioning and PAOprocessor 1900 may maintain different control algorithms for thecontroller 1504 as well as the other controllers 1502 and 1506 in thememory of setpoints 1315 (FIG. 13) so that different control algorithmsand strategies may be selected and implemented for different types andclasses of airplanes which are being serviced.

FIG. 7 presents a schematic diagram of the post-cool air conditioner522. With reference to FIG. 7, a compressor 702 compresses therefrigerant and sends it along a path 704 to one of the pair ofcondenser coils 410, where the refrigerant is cooled by air flowingthrough the air conditioning module 400 under the impetus of thecondenser fan 414, as was described above, where the refrigerant coolsand becomes liquefied. The air conditioning and PAO processor 1900 (FIG.19) sends out a first on/off post-cool shutoff signal to a solenoidvalve 703 and an on/off post-cool compressor on signal 1704 which canturn the post-cool compressor 702 on and off (see FIGS. 18 and 19) andwhich can shut down the post-cool air conditioner 522 by shutting offthe compressor 702 and isolating the compressor 702 from refrigerantmigration by closing the solenoid valve 703. The shutdown algorithm willthen close all the refrigeration valves 720, 738, and 732 (FIG. 7) tofurther prevent refrigerant migration back to the compressor 702.

The cooled and liquefied refrigerant next flows past a charging valve708, a filter dryer 706, and a sight glass 710 over a path 712 to abrazed plate heat exchanger 714 (FIGS. 4 and 7) that is mounted at thevery bottom of the air conditioning module 400, as is shown at 714 inFIG. 4. The brazed plate heat exchanger 714 has a multi-purpose design:it serves as a liquid refrigerant accumulator that collects any excessliquid refrigerant and any excess oil that may be in the suction linebetween the compressor 702 and the evaporator array 514, preventingdamage to the compressor 702 (which is designed to pump vapor). Thebrazed plate heat exchanger 714 also serves as a liquid suction linesub-cooler that sub cools the liquid refrigerant by allowing theexpanded gasses flowing along the path 728 and 730 and entering thecompressor 702 to absorb heat from the liquid refrigerant in the line712 and 718 and in the brazed plate heat exchanger 714. The liquid lineside of the brazed plate heat exchanger 714 acts as a refrigerantreceiver, accumulating excess refrigerant charge on the condenser sideof the system. The brazed plate heat exchanger 714 increases thecapacity and efficiency of the cooling system at high load conditions.Finally, the brazed plate heat exchanger is used to control the suctionline superheat, allowing the evaporators to be fully flooded. Floodingthe evaporators allows high cooling capacity from the evaporators aswell as increasing the evaporator capacity while maintaining higherrefrigerant temperature which helps avoid evaporator frosting.

The path 718 conducts the cooled but still liquefied refrigerant to anelectronically controlled expansion valve 720 that is controlled by a0-to-10 volt signal generated by the processor 1900. The liquidrefrigerant flows through the expansion valve 720 into the low pressure,cool side of the refrigerant circuit, where the liquid begins tovaporize and absorb heat from its surroundings. This boiling liquidflows to the plate fin evaporator array 514, shown in FIGS. 9 and 10,where the refrigerant cools the air that is blown out through the airduct 26 to the airplane (not shown). The gaseous refrigerant leaves theplate fin evaporator array 514 and flows along the path 728 back throughthe brazed plate heat exchanger 714 and over the path 730 back to thecompressor 702 where it is once again compressed and fed into the pairof condensers 410 to be cooled and liquefied, thus completing thepassage all the way through this circular refrigerant circuit.

Combined temperature and pressure transducers monitor the condition ofthe refrigerant throughout this circuit. An RTD temperature and pressuretransducer 707 monitors the temperature and pressure of the liquidrefrigerant as it leaves the pair of condensers 410 and enters thebrazed plate heat exchanger 714. A second RTD temperature and pressuretransducer 716 monitors the temperature and pressure of the liquidrefrigerant as it leaves the brazed plate heat exchanger 714 over thepath 718 and flows through the electronic expansion valve 720. Anothertemperature and pressure transducer 734 monitors the temperature andpressure of the gaseous, cooled refrigerant flowing out of the plate finevaporator array 514. A pair of temperature and pressure transducers 709and 711 monitors the temperature and pressure of the gaseous refrigerantentering the compressor 702 and also leaving the compressor 702. Therefrigerant temperature and pressure readings generated by all of thesetransducers 707, 716, 734, 709, and 711 and also the post-cool condenserair output temperature measured by the RTD air temperature transducer544 are fed into the air conditioning and PAO processor 1900 (see FIG.19) where these temperatures and pressures may be stored in the data log1319 (FIG. 13).

The refrigerant temperatures measured by the RTD temperature transducers709, 716 and 734 and the air temperature measured by the pre-cool airconditioner RTD output temperature transducer 544 are also used for airconditioner control purposes, as is illustrated in FIG. 15.

The pre-cool air conditioner output temperature measured by the RTDtemperature transducer 544 is compared to a setpoint temperature,typically 10 degrees Celsius or thereabouts, by means of a controller1512 which is implemented as a digital process control algorithm withinthe air conditioner and PAO processor 1900. As the desired outputtemperature is adjusted by the user, this setpoint temperature can bealtered. This controller 1512 is given both proportional and integraloutputs which are summed and used (as a 0-to-10 volt signal) to controlan electronic exhaust gas bypass valve 738 (EGBV—FIGS. 7 and 15) which,to the degree it is open, permits compressed, hot gas to bypass the pairof condenser coils 410 and the expansion valve 720 and to flow directlyfrom the compressor 702 into the evaporator array 514, thereby raisingthe temperature and boiling excess refrigerant liquid within theevaporator array 514. The processor 1900 continuously adjusts this EGBvalve 738 to maintain the air temperature at the pre-cool airconditioner's plate fin evaporator array 514 outlet at or just abovefreezing so that the evaporator array 514 is not permitted to ice up.

The refrigerant temperature (measured by RTD transducer 716) at theoutlet of the electronic expansion valve (EEV) 708, which is the inletinto the plate fin evaporator array 514, is fed into another controller1508 (FIG. 15), which is also implemented as a digital process controlalgorithm within the air conditioner and PAO processor 1900. Thiscontroller 1508 is also given both proportional and integral outputswhich are summed and used (as a 0-to-10 volt signal) to control anelectronic evaporator array pressure regulator valve EPR 732 (FIGS. 7and 15) which valve controls how much cooled, expanded, gaseousrefrigerant is permitted to enter the compressor 702. In this manner,the temperature at the input to the evaporator array 514 is controlledand maintained at a setpoint value Tsp, which value is fed into thecontroller 1508 (FIG. 15). This setpoint is typically kept at 1 degreeCelsius. As the desired unit output temperature is adjusted by the user,the setpoint may be altered. The air conditioning and PAO processor 1900maintains this setpoint value, as well as other similar temperature andpressure setpoint values, in a memory for setpoints 1317 (FIG. 13) wherethese values may sometimes be altered when different types and classesof airplanes are being serviced.

The refrigerant temperature (measured by RTD transducer 716) at theoutlet of the electronic expansion valve (EEV) 708, which is the inletinto the plate fin evaporator array 514, is compared to the refrigeranttemperature (transducer 734) at the outlet of the plate fin evaporatorarray 514 by another controller 1510, which is also implemented as adigital process control algorithm within the air conditioner and PAOprocessor 1900. This controller 1510 may initially be given bothproportional and integral outputs which are summed and used (as a0-to-10 volt signal) to control the electronic expansion valve EEV 708(FIGS. 7 and 15) which valve controls to what extent the entireevaporator array 514 is thoroughly wetted and participating in thecooling process. Experiments have shown, however, that the controller1510 may have to be programmed in a nonlinear manner, with the controlparameters worked out empirically by experiment and varying from asimple proportional and integral controller to some degree. The EEV 708is adjusted to maximize the effective cooling area of the evaporatorarray, as is indicated by a maximum temperature drop across the platefin evaporator array 514. The air conditioning and PAO processor 1900may maintain different control algorithms for the controller 1510 aswell as the other controllers 1512 and 1508 in the memory of setpoints1315 (FIG. 13) so that different control algorithms and strategies maybe selected and implemented for different types and classes of airplaneswhich are being serviced.

The compressors 601 and 702 are part number ZR300-KCE-TWD-250 ofCopeland, Sidney, Ohio. The suction line subcoolers or brazed plate heatexchangers 614 and 714 are part number AA6259 of SWEP International,Landskrona, Sweden. Pressure transducers are part number MX5018 providedby Gems Sensors & Controls, Plainville, Conn. The pairs of 60″ by 34″preassembled microchannel condenser coils 406 and 410 are part number26944 D13 custom assembled by Trilectron Industries, Palmetto, Fla.

Clearly, the proper operation of the air conditioner components justdescribed is dependent upon the proper operation of many air andrefrigerant temperature and pressure measurements. If any of themeasurement instruments fail, the air conditioners 520 and 522, underthe control of the air conditioning processor 1900, tries to continueoperating, with warning messages, substituting for actual temperatureand pressure measurements historical temperature and pressuremeasurements recorded on earlier days when the ambient weatherconditions and the type or class of airplane were the same. In thismanner, the air conditioning system continues to operate even when someof its sensors and controllers are inoperative.

A major advantage of the air conditioning system just described is itsability to enter a fully operative state, providing full pressure of aircooled to the proper temperature, within 20 seconds or so of when it isfirst started up, rather than several minutes later as in conventionalair conditioning airplane ground support equipment.

As explained above, the PAO liquid coolant system 700 derives itscooling from the heat exchanger 602 which is part of the pre-cool airconditioner 520. The PAO system 700 does not derive its cooling from thepost-cool air conditioner 522. Accordingly, when the PAO system is inoperation, it reduces the cooling capacity of the pre-cool airconditioner 520. The post-cool air conditioner 522 may be adjustedupwards in the amount of cooling which it provides to the air flowingthrough the air duct 26 to the airplane so that the turning on and offof the PAO system 700 does not necessarily alter the temperature andpressure of the cooled and dehumidified air provided to the airplane bythe air duct 26.

The PAO cooling system 700 is illustrated schematically in FIG. 8. Mostof the elements of the PAO cooling system are positioned within the airconditioning module 400 near the top of that module, adjacent to thepair of PAO liquid coolant conduits 28 shown in FIGS. 1 and 2 thatconvey the PAO liquid to and from the airplane to shorten the length ofthe PAO liquid coolant conduits 28 as much as possible. A PAO liquidreservoir 803 is positioned lower down within the module 400 to serve asa reservoir for reserve amounts of the PAO liquid coolant.

With reference to FIG. 8, a PAO fluid pump 805 pumps PAO fluid through afirst check valve 807 and through a second check valve 809 to the heatexchanger 602, which is part of the pre-cool air conditioner 520, as wasexplained above. The cooled PAO fluid then flows onwards over a path 811through filters 813 and over a path 817 to a supply solenoid valve 819that is turned on and off by the processor 1900 (FIG. 19). When thevalve 819 is open, the PAO fluid flows over a path 820 out of the airconditioning module 400 and over a conduit 822 into an airplane 823where it flows through and cools electronics and avionics components825.

The PAO fluid then flows over a second conduit 824 back from theairplane 823 to the air conditioning module 400 and over a path 826 thatleads to the PAO liquid reservoir 803 where it collects, waiting to bedrawn back out by the pump 828 and sent back to the heat exchanger 602again. That completes the PAO liquid coolant circuit.

The PAO liquid coolant collects in the liquid reservoir 803. A liquidlevel sensor 824 signals to the air conditioning and PAO processor 1900(FIG. 19) when the liquid level is too low. When the PAO system iscabled up to an airplane, there is typically air in the conduits 822 and824 and possibly in the electronics and avionics as well. When the PAOsystem is first turned on, the solenoid valve 819 is opened and then thePAO pressure is slowly raised up to the proper operating pressure. Anyair present in the system collects above the liquid in the reservoir803, and a vacuum pump 833, actuated by the air conditioning and PAOprocessor 1900 (FIG. 19), pumps this air out of the liquid reservoir803. This prevents overheating of the electronics and avionics 825caused by air displacing the PAO liquid coolant in the circulatingsystem.

A 3-way proportional flow regulator valve 828 (FIGS. 8 and 15) controlsand continuously adjusts a liquid coolant bypass path 829-830 thatbypasses the heat exchanger 602 with some of the PAO liquid to reducethe cooling effect. The regulator 828 receives temperature signalsdirectly from a temperature and pressure sensor transducer 832.Alternatively, the processor 1900 can implement a digital controllerwhich can compare the temperature measured by the transducer 832 to anadjustable setpoint temperature and then adjusts the regulator valve 828accordingly.

A bypass path 834 is controlled by an electronically controlledproportional flow restriction valve 821 having a pressure setpoint thatcan be set and varied by the air conditioning and PAO processor 1900. Asis illustrated in FIG. 15, a controller 1516 compares the PAO systemoutput pressure, as measured by the temperature and pressure sensingtransducer 832, to a setpoint pressure Psp (stored in the memory forsetpoints 1317 (FIG. 13) and then amplifies the pressure differenceusing proportional and integral control functions to generate controlsignals which are summed and then fed as a control signal to theelectronically controlled proportional flow restriction valve 821. Thecontroller 1516 can be implemented as a control algorithm within the airconditioning and PAO processor 1900. The pressure setpoint Psp may bevaried in accordance with the specific needs of different types andclasses of airplanes being serviced in response to airplane selectionusing the main menu shown in FIG. 21. It is also possible to have therestriction valve 821 respond directly to pressure indicating signalsfrom the transducer 832 without the use of the processor 1900 and thecontroller 1516, and this is the arrangement actually shown in FIG. 8(for this reason, FIG. 19 does not presently show an output signal fromthe processor 1900 leading to the valve 821).

To protect the PAO system 700 from transients, a bypass valve 835 can beactuated by excessive pressure sensed by the transducer 832 and openedto bypass the heat exchanger 602, pump 805, and reservoir 803. Thecontroller 1516, implemented within the processor 1900, opens the bypassvalve 835.

A PAO hydraulic manifold assembly, part number AGA15700-0-C, whichincludes the components 819, 821, and 835, can be obtained from theRexroth Bosch Group. The PAO pump 833, Model 4600-20, comes from McNallyIndustries, Grantsburg, Wis. The PAO heat exchanger 602 is part numberAA 6283 of Swep International, Landskrona, Sweden. The PAO pump pressurerelief system is part number a971207 zc 04a2 is supplied by SunHydraulics, Sarasota, Fla.

To increase the efficiency and also to decrease the size of theevaporator arrays 504 and 514, in one embodiment these evaporator arraysare each constructed from four automotive plate fin evaporator arrays802, 804, 806, and 808 (FIGS. 9 and 10) assembled into a roughly squareframe 810 and held in place by a cover plate 812. The assembled frame810 and plate fin evaporator arrays 802-808 shown in FIG. 8 is used toconstruct each of the two evaporator arrays 504 and 514. The evaporatorarray 514 is shown in FIGS. 9 and 10 attached to an incoming expansionchamber or air funnel 513 (FIG. 9) which accepts air flowing out of theblower 508 and spreads this air out in a uniform manner over the surfaceof the four plate fin evaporator arrays 802-808 to maximize the coolingefficiency of this unit. Air flows out of the evaporator array 514 intoa second funnel 516 which ducts the air to an outgoing cooled air port518 to which is attached the air duct 26 (FIGS. 1, 2, 4, and 5) thatconveys the cooled air to the airplane. The evaporator array 504 (notshown in FIGS. 8 and 9—shown in FIGS. 4 and 5) receives outside air 501that flows through the air filter 502 directly into the evaporator array504. Air flows out of the evaporator array 504 through a funnel 505(FIG. 4) directly into the blower 508. The plate and fin design of theevaporator arrays 504 and 514 allows them to be inexpensive, compact,and highly efficient.

To decrease the size and increase the efficiency of the condenser coils406 and 410, each condenser is constructed from a pair of overlaid andinterconnected microchannel condenser coils. With reference to FIG. 4,these pairs of condenser coils 406 and 410 are long and wide enough tobe mounted on the panels or door assemblies 404 and 408. The door 404may be swung open to give convenient access to the other mechanical airconditioning components within the module 400, as is shown. The pairs ofcondenser coils 406 and 410 are quite thin, so they do not take up muchroom within the air conditioning module 400, unlike prior tube and finarrangements which were much more bulky.

With reference to FIGS. 11 and 12, the microchannel condenser coils(used in pairs to construct the condenser coils 406 and 408) are eachconstructed as a pair of parallel, spaced-apart refrigerant pipes 1002and 1004 having narrowed or tapered end sections 1006 and 1008 forconvenient attachment to copper or flexible tubing. Hollow, rectangularducts 1010 are mounted between and perpendicular to the pipes 1002 and1004, with the ends of the ducts 1010 passing through slots cut partwaythrough the sides of the pipes 1002 and 1004, as is best shown in FIG.12. The rectangular ducts 1010 are further partitioned internally bypartitions 1012 into very small, rectangular channels that provide pathsthrough which the refrigerant may pass between the two pipes 1002 and1004 flowing through the ducts 1010. The spaces between the rectangularducts 1010 are then filled in with folded, thin aluminum fins foldedaccordion style to maximize heat transfer between the air flowingthrough the microchannel condenser coil and the refrigerant flowing fromthe pipe 1002 to the pipe 1004. These aluminum fins, as well as thearrangement of pairs of condenser coils, force the air to travel azigzag course, and this further adds to the efficiency of the design.

Further details concerning the general design of such microchannelcondenser coils may be found in U.S. Pat. No. 6,988,538 which issued toJustin P. Merkys, et al. on Jan. 24, 2006.

Referring now to FIG. 13, all of the modules 14, 20, 22, 400, and 1308are shown to be networked together by a network 1312, which in oneembodiment is realized using a CAN bus, developed by CIA (CAN InAutomation), Erlangen, Germany. Clearly, other bus protocols can also beused, including Ethernet and TCP/IP to network these componentstogether. The CAN bus is one designed particularly for use in a hostile,automotive, outdoors environment. The control module 22 communicateswith the can bus network 1312 using a cart network bus driver 1310, andall the other module-based processors do likewise (not shown in FIG.13).

The control module 22 is shown to have a display screen 24 that has anarray of four pushbuttons 1302 to its left and a second array of fourpushbuttons 1304 to its right, aligned with menu selections on displayedimages (see menus and submenus, FIGS. 21-28). The menus are storedwithin a universal control and diagnostic processor 1306 which managesthe display screen 24 and also manages some diagnostics tasks and thelike. The processor 1306 inquires over the bus network 1312 as to whichmodules are present, and it tailors the displayed informationaccordingly. Menus and diagnostics are not displayed for any module thatis not present and operating.

A hierarchical arrangement of one possible set of menus and otherdisplays is shown in FIG. 20. When the system is first turned on, a mainscreen or menu (shown in detail in FIG. 21) is displayed. This main menupermits the operator of the cart 10 to simply select which of severalairplanes the ground support equipment cart is to service. If theoperator depresses the pushbutton adjacent the “T-50 Golden Eagle” item,a secondary menu shown in FIG. 23 is displayed. When the operatordepresses the pushbutton adjacent the “Start” item, the airconditioners, one of the power sources, and the PAO liquid coolingsystem are all started up. The processor 1306 conveys to the processorswithin other modules, and in particular the air conditioner and PAOprocessor 1900, the identity of the plane that is to be serviced (theT-50), and this allows, for example, the air conditioner and PAOprocessor to adjust the setpoints 1317 that control the operation of thetwo air conditioners and the PAO system in accordance with thespecialized needs of the T-50 class of airplanes. FIG. 15 illustratesmany of the temperature Tsp and pressure Psp setpoints whose settingsmay be adjusted in this manner to adapt the equipment on the cart 10 tothe needs of particular types and classes of airplanes.

The operator may return to the main menu (FIG. 21) and depress thepushbutton adjacent “Maintenance,” and then a maintenance menu isdisplayed (FIG. 25). From this maintenance menu, one may navigate to aData Log display (FIG. 26) where one may scroll through a log oftemperatures, pressures, and other data gathered over time. This datalog information 1319 (FIG. 13) is also available for further processingby the universal control and diagnostics processor 1306 which cangenerate reports predicting such things as when certain components willrequire service or are likely to fail. For example, a gradual increasein the differential pressure across the air filter 502 measured by thedifferential pressure sensor 528 would enable one to predict when thefilter 502 will have to be cleaned or replaced. Other similarmaintenance and repair prediction reports can be generated in thismanner by the diagnostic processor 1306. The data log 1319 is maintainedby processors (such as the processor 1900) within each module, so thatthis information stays with each module if the modules are moved aboutand separated.

Other more focused maintenance reports may be displayed. For example apre-cool air conditioner status report (FIG. 27) indicates the currentstatus of the air conditioner 520, indicating such useful things as howmuch refrigerant is currently bypassing the pair of condenser coils 406by flowing through the bypass valve 638 to reduce the temperature of theevaporator array 504, as was explained above. The current settings ofthe expansion valve 620 and of other valves and the speed of thecondenser fan 414 are also indicated, along with the on/off state of thetwo compressors 601 and 702.

Help menus are also provided, as is shown in the illustrative menusshown in FIGS. 22 and 24.

FIG. 29 presents some mechanical details of the display screen 24. Thedisplay screen 24 is a black-and-white, electroluminescent display thatis fully operable over extreme ranges of temperature. The display screen24 is sandwiched together with a metal screen 2902 and with a protectiveplastic cover plate 2904 all of which are mounted to the side of thecontrol module 22 facing an operator standing before the cart 10. Thescreen 2902 provides radio frequency shielding to the display,preventing signals from leaking either into the control module 22 or outof the control module 22. This rugged, simple arrangement of anall-weather display and eight rugged pushbuttons 1302 and 1304 providesan all-weather display that combines many displays and controls which,in prior designs for ground support equipment carts, were scattered allover the cart, with separate gauges and controls for each appliance, andwith no uniformity of control.

Referring now to FIG. 14, the state machine of a master process 1400 forthe air conditioner and PAO processor 1900 is shown. When power isapplied to the module 400, the processor 1900 initiates a boot sequence1402 that prepares the processor 1900 for operation. The boot sequence1402 enables the processor 1900 to determine whether it is configured asa “stand-alone” or “cart-mounted” module. If the module 400 is cartmounted, it waits (at step 1406) for the start command to come in fromthe CAN data bus after actuation of a START menu command on anairplane-specific menu such as that shown in FIG. 23. Otherwise, theprocessor 1900 seeks discrete signals from its own more primitive userinterface (possibly a portable computer plugged into the module 400using an Ethernet, CAN, or USB portal.

After the boot sequence 1402, the processor 1900 enables a data loggingsub-machine 1404. The data logging sub-machine 1404 receives presentsensor signals from the module 400 and records them in the data log1319. This data log is used by the processors 1900 and 1306 forpredictive failure and for enhanced diagnostic functioning, as has beenexplained.

After the processor 1900 enables the data logging sub-machine 1404, itenters an idle state at 1406. In the idle state 1406, the processor 1900waits for an “On” command to arrive, as from the “Start” command on theairplane-specific menu shown in FIG. 23. This “On” command may come fromthe CAR data bus or the user interface of the module 400. After theprocessor 1900 receives the “On” command, it exits the idle state 1406and enters the check power state at 1408.

In the check power state 1408, the processor 1900 performs a self test.Stored default parameters or menu-selected operating parameters aregiven to the processor 1900 at power up. These operating parameters setthe setpoint 1317 temperatures and pressures that the processor 1900desires to achieve (see the values Tsp and Psp shown in FIG. 15). Theseoperating parameters are adjusted to those appropriate to the outputtemperatures and pressures (and electrical power) required by any givenairplane that may need to be connected to the air conditioning and PAOmodule 400. After the check power state is done, the processor 1900stages the compressors 601 and 702 and the blower 508 on to assure thatthe air conditioner output temperature (measured by the transducer 544)is not permitted to exceed an undesired level. Additionally, theprocessor 1900 stages all of the remaining big loads on to prevent unduetransient loading of the electrical source of power. Thus, the PAOsystem 700 is gradually brought up to pressure and down in temperature,and the vacuum pump 833 clears the PAO system of air before it comesfully on line.

While in the check power state 1408, the processor 1900 alsoauto-detects the input power type (using transducers 1708 to 1718 shownin FIG. 18) and varies the two air conditioners' 520 and 522 and the PAOsystem's 700 settings accordingly, degrading the maximum obtainableperformance to reflect less power availability or the need to providePAO cooling in addition to air cooling. For example, if the processor1900 detects a lower input voltage than a desired input voltage on thetransducers 1710, 1712, and 1716, the processor 1900 may adjust thesetpoints 1317 to provide less cooling to the airplane to compensate forthis. This automatic response to changing power conditions allows theuser seamless use of the unit regardless of the city or country in whichthe unit is being operated.

If the processor 1900 senses no power or abnormal power for ten seconds,it disables any machines presently running, attempts to isolate thepower fault, and then enters a system fault triggering alarm state 1422.Such a system fault is announced with an audible and visible alarm. Solong as any power is available to it, the processors 1900 and 1306continue operate, allowing isolation of the fault and continued use ofthe remainder of the modules. Capacitors that momentarily store chargeprovide brief continued running time for the processors 1900 and 1306following a power failure. In an alternative arrangement, back-upbatteries could be provided within each module to provide the moduleprocessors with continued power to operate and to perform diagnosticswhen power is not available for some reason.

If adequate power is available, the processor 1900 enters the enablesub-state machines state 1410 where it starts up various real-timebackground processes. From the state 1410, the processor 1900 proceedsto the run state 1412. In the run state 1412, the processor 1900commences normal operation. Under normal operation, the processor 1900achieves the desired output parameters (the given setpoint temperaturesand pressures) as efficiently as possible by staging the condenser fan414 to slow and fast settings and by adjusting the air conditioning andPAO parameters to produce the desired output. The selected parameters orsetpoints are utilized as is shown in FIG. 15, where the controllers1502, 1504, 1506, 1508, 1510, 1512, 1514, and 1516 are all implementedas process control digital algorithms executing as control chainsinstituted within the air conditioning and PAO processor 1900 such thateach controller implements a control chain within the processor 1900that becomes part of one of the feedback control loops shown in FIG. 15within the two air conditioners 520 and 522 and the PAO system 700. Datalog processing continues during this normal operation of the processor1900.

Maintenance and diagnostics are also carried out by the two processors1900 and 1306. The data log 1319 is collected for use in predictivefailure and enhanced diagnostics. In the event of a minor componentfailure or imminent major component failure, the processor 1306 enters afail safe state 1418. If, based on the data collected, there is a dangerof continued operation, the processor 1306 announces a fatal systemfault and enters the alarm state 1422 and immediately shuts down theunit at 1420. If the data log 1319 indicates that the unit is operatingoutside of its normal operating range, the processor 1306 announces asystem fault and enters the alarm state 1422 but does not necessarilyshut down the entire module 400. If the data log 1319 indicates that aproblem may occur in the near future, the processor 1306 may simplyannounce a systems warning and enter the fail safe state 1418. The failsafe state 1418 does not sound an alarm, but it shows an indication onthe display 22 as to the nature of the warning. The alarm 1422, failsafe 1418, and shutdown 1422 states may be entered from all other states1416 in the master process 1300 of the processor 1900.

The controller continues normal operation in the run state 1412 until itreceives an “Off” or “Stop” command, typically from one of the menusshown in FIGS. 21, 23, and 25. After receiving the “Off command,” theprocessor 1900 enters the disable sub-state machines state 1414. Whilein this state 1414, the processor 1900 winds down the operation of allof the system components and stores any data log 1319. The processor1900 then returns to the idle state 1406 and awaits another “On” or“Start” command.

Referring now to FIG. 16, a processor 1900 implemented state machine1501 for one of the compressors 601 or 702 is shown. The compressorstate machine 1501 begins in an idle state 1503. Once the processor 1900enables the compressor state machine 1501 and there is no current fault,the compressor state machine 1501 enters the wait state 1505. While inthe wait state 1505, the compressor state machine 1501 runs a shortcycle timer to produce a delay. Once the short cycle timer reaches zero,the compressor state machine 1501 moves from the wait state 1505 to thestarting state 1507 and starts the compressor 601 or 702. While in thestarting state 1507, the compressor state machine 1501 pauses for thirtyseconds before advancing to the running state 1509.

The compressor state machine 1501 remains in the running state 1509, andthe compressor 601 or 702 continues to operate, until the processor 1900signals for the compressor to be disabled. Once the compressor disablecommand is received, the compressor state machine 1501 moves from therunning state 1509 to the shut down state 1511. The compressor statemachine 1501 may be signaled that the compressor has been disabledduring any normal state 1513 in case of a system fault. Upon receipt ofsuch a signal, the compressor state machine 1501 enters the shut downstate 1511. Finally, from the shut down state 1511, the compressor statemachine 1501 reenters the idle state 1503.

Referring now to FIG. 17, the blower 508 state machine 1600 is shown.The goal of the blower state machine 1600 is to achieve the desired flowrate of air and pressure to meet the operating parameters of any givenairplane by controlling the variable speed impeller located within theduct of the two air conditioners. The blower 508 begins in an idle stateat 1602. Once the processor 1900 enables the blower state machine 1600and provides a pressure operating setpoint, the blower state machineenters a first of two troubleshooting states 1604. In this state, theimpeller is set to low speed to troubleshoot any initial problems, suchas a blockage or failure of the blower 508 to operate. The blower statemachine 1600 then enters a second troubleshooting state 1606 in whichchecks of pressure and power to the blower 508 are run to see if an airduct 26 is connected between the cart 10 and an airplane or if, in someother respect, there is bad pressure. If no air duct 26 is connected, orif the air duct 26 is connected to the wrong type or class of airplane,or if sensors on the blower system otherwise sense bad pressure readingsfor ten seconds, the blower state machine 1600 will enter the alarmstate 1622, giving forth an appropriate warning to the operator.

If an air duct 26 is connected and there is otherwise good pressure, theblower state machine 1600 will enter the adjust blower motor frequencystate 1610. Here the motor 506 A.C. power frequency is set. The blowerstate machine 1600 then enters a state 1608 where it checks the pressurechange across the blower 508. If no air duct 26 is connected, or if theair duct 26 is connected to the wrong type or class of airplane, or ifsensors on the blower system otherwise sense bad pressure for tenseconds, once again the blower state machine 1600 enters the alarm state1622, giving forth an appropriate warning to the operator. If an airduct 26 is connected and if there is good pressure, and if a type orclass of airplane has been selected using the menu shown in FIG. 21,then the pressure change across the blower 508, measured by thedifferential pressure sensor 532 (FIG. 5), and the power consumed by theblower voltage-to-frequency converter 525, measured by multiplying thevoltage 1720 by the current 1722 (FIG. 18), are compared to normallogged values found in the data log 1319 for the type or class ofairplane that was selected on the menu shown in FIG. 21. If the pressureand power consumed do not correspond to that type of airplane, then theoperator is given an alarm 1622 and the idle state 1602 is entered whilethe problem is checked out.

The blower state machine 1600 next checks the blower map 1612. Theblower map contains data that helps guide and shape the controlalgorithm within the processor 1900 that sets the blower motorfrequency. This data sets the operational limits of the blower systemand also includes information assessing the health of the blower system.

If the status data of the blower 508 is contained within the blower map,the blower state machine 1600 enters a state 1614 where the blower 508is permitted to run at a given frequency while the deviation of the cart10 output pressure (as measured by the pressure transducer 526) ischecked. If the deviation or error exceeds a threshold value (step1650), then the blower frequency is once again adjusted at step 1615 tominimize the error.

If, at step 1612, data for the blower is not found within the blowermap, the blower state machine 1600 enters the alarm state 1422 and shutsdown the air conditioners.

FIG. 18 presents a partly block and partly schematic diagram of thesignal and electrical power connections to the compressors 601 and 702,the two speed condenser fan 414, and the blower 508, its motor 506, andits voltage-to-frequency converter 525. The locations of voltage andcurrent sensors are shown, all of which feed signals into the airconditioning and PAO processor 1900 shown in FIG. 19. Signals generatedby the processor 1900 (shown in FIG. 19) and fed into the components601, 702, 414, and 525 are also shown in FIG. 18 to complete thedisclosure of all significant signals connecting the processor 1900 tothe various air conditioning processes.

FIG. 19 presents the air conditioning and PAO processor 1900. FIG. 19reveals and lists and categorizes all of the signals that flow fromvarious types of sensors associated with the air conditioning processesand the PAO process into the processor 1900. It also reveals and listsand categorizes all of the control signals generated by the processor1900 that flow back to and that control the components of the airconditioning processes and the PAO process. In FIG. 19, all the signalsare identified by name and by the same reference number that is assignedto the transducer that is the source of an incoming signal or to thedevice that is the target of an outgoing signal. “PRE-C” is a signalrelating to the pre-cool air conditioner 520 shown primarily in FIG. 6.“POST-C” is a signal relating to the post-cool air conditioner 522 shownin FIG. 7. “PAO” is a signal relating to the PAO liquid coolantprocessor shown in FIG. 8. Many of the signals shown in FIG. 19 whichrelate to the actual control of processes are also shown in the processcontrol diagram presented in FIG. 12. Other signals originate in or goto FIG. 18. The use of these signals has already been explained above.

While an embodiment of the invention has been disclosed, those skilledin the art will recognize that numerous modifications and changes may bemade without departing from the true spirit and scope of the claims asdefined by the claims annexed to and forming a part of thisspecification.

1. A fluid cooling system for airplane electronics which detachablyconnects to a first port and a second port on an airplane, the coolingsystem comprising: a first connector, a second connector, and a fluidconduit therebetween, the first and second connectors being adapted tobe connected to the first and second ports, respectively, and whereinsuch connection of the ports to the connectors completes a fluidcircuit; a fluid pump that directs fluid through the fluid conduit; afirst bypass that redirects fluid past the first and second connectorsand the airplane to stabilize the pressure applied across the first andsecond connectors. a heat exchanger that removes heat from the fluid inthe fluid conduit; and a temperature regulation mechanism thatstabilizes the temperature of the fluid in the fluid conduit tocompensate for changes in the amount of heat drawn from the airplaneelectronics.
 2. A fluid cooling system in accordance with claim 1further comprising a pressure sensor arranged to sense the pressure offluid across the connectors and generating a pressure indication signal;and a pressure comparator that compares the pressure indication signalto a setpoint pressure chosen in accordance with the requirements of thetype and class of the airplane and that generates a pressure comparisonsignal which is fed to the first bypass to control its redirectionactivities.
 3. A fluid cooling system in accordance with claim 2 furthercomprising a plurality of fluid setpoint pressures in a memory eachcorresponding to the needs and requirements of different types orclasses of airplanes, a display on which the different types or classesof airplanes are identified for manual selection by a human operator,and a control system that responds to manual selection of a particulartype or class of airplane by retrieving the setpoint pressurecorresponding to that airplane from the memory and conveying thatsetpoint pressure to the pressure comparator.
 4. A fluid cooling systemin accordance with claim 1 wherein the temperature regulation mechanismcomprises a second bypass connected in parallel with the heat exchangerand controlled by the temperature regulator mechanism to bypass the heatexchanger as needed to regulate the temperature of the fluid.
 5. A fluidcooling system in accordance with claim 4 further comprising a pressuresensor arranged to sense the pressure of fluid applied across theconnectors and generating a pressure indication signal; and a pressurecomparator that compares the pressure indication signal to a setpointpressure chosen in accordance with the requirements of the type or classof airplane and that generates a pressure comparison signal which is fedto the first bypass to control its redirection activities.
 6. A fluidcooling system in accordance with claim 5 further comprising a pluralityof setpoint pressures in a memory each corresponding to the needs andrequirements of a different type or class of airplane, a display onwhich the different types and classes of airplanes are identified formanual selection by a human operator, and a control system responsive tomanual selection of a particular type or class of airplane forretrieving the setpoint pressure corresponding to that type or class ofairplane from the memory and conveying it to the pressure comparator. 7.A ground support equipment cart having an air conditioning system for anairplane and also having a fluid cooling system for airplane electronicswhich cooling system detachably connects to a first port and a secondport on an airplane, the fluid cooling system comprising: a firstconnector, a second connector, and a fluid conduit therebetween, thefirst and second connectors being adapted to be connected to the firstand second ports, respectively, and wherein such connection of the portsto the connectors completes a fluid circuit; a fluid pump that directsfluid through the fluid conduit; a heat exchanger in the fluid conduitthat removes heat from the fluid circuit and transfers it into the airconditioning system of the ground support equipment cart; and atemperature regulation mechanism that stabilizes the temperature of thefluid in the fluid conduit to compensate for changes in the amount ofheat drawn from the airplane electronics.
 8. A ground support equipmentcart in accordance with claim 7 further comprising: a first bypass thatredirects fluid past the first and second connectors and the airplane tostabilize the pressure applied across said first and second connectors.9. Aground support equipment cart in accordance with claim 8 furthercomprising a pressure sensor arranged to sense the pressure of fluidacross the connectors and generating a pressure indication signal; and apressure comparator that compares the pressure indication signal to asetpoint pressure chosen in accordance with the requirements of the typeand class of airplane and that generates a pressure comparison signalwhich is fed to the first bypass to control its redirection activities.10. A ground support equipment cart in accordance with claim 9 furthercomprising a plurality of fluid setpoint pressures and air conditioningsetpoint pressures in a memory each corresponding to the needs andrequirements of different types and classes of airplanes, a display onwhich the different types and classes of airplanes are identified formanual selection by a human operator, and a control system that respondsto manual selection of a particular type or class of airplane byretrieving the fluid and air conditioning setpoint pressurescorresponding to that type and class of airplane from the memory andconveying the fluid setpoint pressure to the pressure comparator and theair conditioning setpoint to the air conditioning system.
 11. A groundsupport equipment cart in accordance with claim 8 wherein thetemperature regulation mechanism comprises a second bypass connected inparallel with the heat exchanger and controlled by the temperatureregulator mechanism to bypass the heat exchanger as needed to regulatethe temperature of the fluid.
 12. A ground support equipment cart inaccordance with claim 11 further comprising a pressure sensor arrangedto sense the pressure of fluid applied across the connectors andgenerating a pressure indication signal; and a pressure comparator thatcompares the pressure indication signal to a setpoint pressure chosen inaccordance with the requirements of the type or class of airplane andthat generates a pressure comparison signal which is fed to the firstbypass to control its redirection activities.
 13. A ground supportequipment cart in accordance with claim 12 further comprising aplurality of fluid setpoint pressures and air conditioning setpointpressures in a memory each corresponding to the needs and requirementsof different types or classes of airplanes, a display on which thedifferent types and classes of airplanes are identified for manualselection by a human operator, and a control system responsive to manualselection of a particular type or class of airplane by retrieving thefluid and air conditioning setpoint pressures corresponding to the typeor class of airplane from the memory and conveying fluid setpointpressure to the pressure comparator and the air conditioning setpoint tothe air conditioning system.
 14. A ground support equipment cart havinga dual, pre-cool and post-cool air conditioning system for an airplaneand also having a fluid cooling system for airplane electronics whichcooling system detachably connects to a first port and a second port onan airplane, the fluid cooling system comprising: a first connector, asecond connector, and a fluid conduit therebetween, the first and secondconnectors being adapted to be connected to the first and second ports,respectively, and wherein such connection of the ports to the connectorscompletes a fluid circuit; a fluid pump that directs fluid through thefluid conduit; a heat exchanger in the fluid conduit that removes heatfrom the fluid circuit and transfers it into the pre-cool portion of thedual air conditioning system of the ground support equipment cart; and atemperature regulation mechanism that stabilizes the temperature of thefluid in the fluid conduit to compensate for changes in the amount ofheat drawn from the airplane electronics, the temperature regulationmechanism also adjusting the parameters of the pre-cool and post-coolportions of the air conditioning system to compensate for the addedcooling load of the fluid cooling system.
 15. A ground support equipmentcart in accordance with claim 14 further comprising: a first bypass thatredirects fluid past the first and second connectors and the airplane tostabilize the pressure across said first and second connectors.
 16. Aground support equipment cart in accordance with claim 15 furthercomprising a pressure sensor arranged to sense the pressure of fluidacross the connectors and generating a pressure indication signal; and apressure comparator that compares the pressure indication signal to asetpoint pressure chosen in accordance with the requirements of the typeand class of the airplane and that generates a pressure comparisonsignal which is fed to the first bypass to control its redirectionactivities.
 17. A ground support equipment cart in accordance with claim16 further comprising a plurality of fluid setpoint pressures and airconditioning setpoint pressures in a memory each corresponding to theneeds and requirements of different types or classes of airplanes, adisplay on which the different types of airplane are identified formanual selection by a human operator, and a control system that respondsto manual selection of a particular type or class of airplane byretrieving the fluid and air conditioning setpoint pressurescorresponding to the type or class of airplane from the memory andconveying the fluid setpoint pressure to the pressure comparator and theair conditioning setpoint to the air conditioning system, adjusting theair conditioning setpoints to reflect whether the fluid cooling systemis or is not in operation.
 18. A ground support equipment cart inaccordance with claim 16 wherein the temperature regulation mechanismcomprises a second bypass connected in parallel with the heat exchangerand controlled by the temperature regulator mechanism to bypass the heatexchanger as needed to regulate the temperature of the fluid.
 19. Aground support equipment cart in accordance with claim 18 furthercomprising a pressure sensor arranged to sense the pressure of fluidapplied across the connectors and generating a pressure indicationsignal; and a pressure comparator that compares the pressure indicationsignal to a setpoint pressure chosen in accordance with the requirementsof the type or class of airplane and that generates a pressurecomparison signal which is fed to the first bypass to control itsredirection activities.
 20. A ground support equipment cart inaccordance with claim 19 further comprising a plurality of setpointpressures and air conditioning setpoint pressures in a memory eachcorresponding to the needs and requirements of different types orclasses of airplanes, a display on which the different types and classesof airplanes are identified for manual selection by a human operator,and a control system responsive to manual selection of a particular typeor class of airplane by retrieving the fluid and air conditioningsetpoint pressures corresponding to that type or class of airplane fromthe memory and conveying the fluid setpoint it to the pressure to thepressure comparator and the air conditioning setpoint to the airconditioning system.